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Optoelectronic devices combining single-layer graphene (SLG) and colloidal semiconducting nanocrystal (NC) heterojunctions have recently gained significant attention as efficient hybrid photodetectors. While most research has concentrated on systems using heavy metal-based semiconductor NCs, there is a need for further exploration of environmentally friendly nanomaterials, such as Cu2−xS. Chemical ligands play a crucial role in these hybrid photodetectors, as they enable charge transfer between the NCs and SLG. This study investigates the photoresponse of an SLG/Cu2−xS NCs heterojunction, comparing the effect of two short molecules—tetrabutylammonium iodide (TBAI) and 3,4-dimethylbenzenethiol (DMBT)—as surface ligands on the resulting structures. We have analysed charge transfer at the heterojunctions between SLG and the Cu2−xS NCs before and after modification with TBAI and DMBT using Raman spectroscopy and transconductance measurements under thermal equilibrium. The photoresponse of two hybrid devices based on three layers of Cu2₋xS NCs, deposited in one case on SLG/Cu2−xS/TBAI ("TBAI-only" device) and in the other on SLG/Cu2−xS/DMBT ("DMBT + TBAI" device), with a TBAI treatment applied, for both, after each layer deposition, has been evaluated under 450 nm laser diode illumination. The results indicate that the TBAI-only device exhibited a significant increase in photocurrent (4 μA), with high responsivity (40 mA/W) and fast response times (<1 s), while the DMBT + TBAI device had lower photocurrent (0.2 μA) and responsivity (2.4 μA), despite similar response speeds. The difference is attributed to DMBT's π–π interactions with SLG, which enhances electronic coupling but reduces SLG's mobility and responsivity. [ABSTRACT FROM AUTHOR]

We propose and numerically investigate a smart, optically transparent digital metasurface reflective in the mmWave range, based on CVD graphene programmable elements. For both TM and TE polarizations, we detail the optimization of the unit cells, designed to exhibit two distinct states that correspond to those of binary encoding. The whole metasurface encoding can be customized to provide different electromagnetic functions, such as wide-band beam splitting at a controlled angle and reduction of the Radar Cross Section. Optically transparent metasurfaces could be integrated and exploited in windows and transparent surfaces in future Beyond-5G and 6G ecosystems. [ABSTRACT FROM AUTHOR]

Hybrid graphene and quantum dots (QDs) photodetectors merge the excellent conductivity and ambipolar electric field sensitivity of graphene, with the unique properties of QDs. The photoresponsivity of these devices depends strongly on the charge transfer at the graphene/QDs interface. Here 1‐pyrene butyric acid (PBA)‐coated PbS QDs with single layer graphene (SLG) are used to investigate the effect of pyrene as a π–π mediator to enhance charge transfer at the SLG/QDs junction under illumination. The surface chemistry at the QD–QD and SLG/QD interface is studied with the conventional tetrabutylammonium iodide (TBAI) QD linker. The hybrid SLG/QD photodetectors with PBA as a SLG‐QD linker demonstrate a photoresponse up to 30% higher than that recorded for devices where only TBAI is used, due to the strong electron coupling between SLG and QDs. Transconductance measurements show that PBA provokes electron depletion in SLG ascribed to the tendency to delocalize the QDs holes, favoring their transfer to SLG. This surface ligand is found to improve the interaction between the QDs light absorbers and the SLG charge collector, leading to an increased photodetection response. This demonstrates that ligand engineering can enhance charge dynamics and boost the performance of the hybrid device. [ABSTRACT FROM AUTHOR]

Graphene is a material with exceptional optical, electrical and physicochemical properties that can be combined with dielectric waveguides. To date, several optical devices based on graphene have been modeled and fabricated operating in the near-infrared range and showing excellent performance and broad application prospects. This paper covers the main aspects of the optical behaviour of graphene and its exploitation as electrodes in several device configurations. The work compares the reported optical devices focusing on the wavelength tuning, showing how it can vary from a few hundred up to a few thousand picometers in the wavelength range of interest. This work could help and lead the design of tunable optical devices with integrated graphene layers that operate in the NIR. [ABSTRACT FROM AUTHOR]

Chemical doping is an effective way to increase the conductivity of graphene. Despite the efforts made by many to achieve p-doping, mainly on CVD graphene, by using a variety of oxidant agents, there is still space to evaluate and optimize methodologies to further reduce the sheet resistance while maintaining high optical transparency. In this study, we developed "new" routes to dope graphene heavily using thionyl chloride that is known to act as chlorinating agent. It was found that, in addition to the nucleophilic reactions replacing oxygen with chlorine, the thermal (T ≥ 120 °C) and pyridine-catalytic activations of the SOCl 2 chemistry result in more p-doping functionalities in the graphene basal plane. A sheet resistance value of 18 Ω/□ was obtained for a 6-layer stacked graphene films with an optical transmittance of 85% at 550 nm. Furthermore, the possibility offered by the plasma oxidation of graphene in a controlled way, allows to introduce in the graphene basal plane the right amount of epoxy and hydroxyl defects so as to maximize the dopant functionalization and, hence, the carrier density, without affecting significantly the carrier mobility. This route allowed to reach a minimum sheet resistance value of 120 Ω/□ for a single layer graphene with 97.5% optical transparency. Image 1 [ABSTRACT FROM AUTHOR]

In this study, we present a two-dimensional dielectric grating which allows achieving high absorption in a monolayer graphene at visible and near-infrared frequencies. Dielectric gratings create guided-mode resonances that are exploited to effectively couple light with the graphene layer. The proposed structure was numerically analyzed through a rigorous coupled-wave analysis method. Effects of geometrical parameters and response to the oblique incidence of the plane wave were studied. Numerical results reveal that light absorption in the proposed structure is almost insensitive to the angle of the impinging source over a considerable wide angular range of 20°. This may lead to the development of easy to fabricate and experimentally viable graphene-based absorbers in the future. [ABSTRACT FROM AUTHOR]

In this paper, we numerically and experimentally demonstrate that few-layer Chemical Vapour Deposition graphene can be employed for the fabrication of fully optical transparent antennas for microwave applications. We show that planar graphene-based antennas, having a size of tens of square centimeters, can achieve relatively high gain over a wide operating bandwidth (>3.5 GHz) simultaneously covering the GPS, WiFi, Bluetooth, and 5G bands. The measured 3D radiation patterns show dipole-, quadruple-, and hexapole-behavior. These findings open up routes for the realization of innovative devices where “invisible and hidden” antennas could be integrated in smart windows or photovoltaic systems, fostering configurations for camouflage, and communications systems. Furthermore, the possibility to handle different radiation patterns could allow the engineering of complex systems such as antenna arrays devoted to beam-steering, beam-forming, and healthcare applications. Finally, combining graphene transparency and flexibility could also pave the way for the realization of wearable devices, demanding invisibility, which operate on the surface of the human body or can be integrated in transparent devices (for example, in contact lenses) reducing their invasiveness. [ABSTRACT FROM AUTHOR]

We demonstrate modulated H 2 and O 2 plasma treatments as an effective methodology for controlled chemical functionalization by hydrogen and oxygen atoms of single- and multi-layer chemical vapor deposition (CVD) graphene aiming at engineering material properties. The effects of the functionalization degree on the optical and transport properties of graphene are discussed with a twofold aim of (i) providing reproducible experimental protocols for tailoring graphene properties, and of (ii) providing insights into the chemical mechanisms involved in the plasma-processing of graphene with hydrogen and oxygen atoms. An unprecedented control over the graphene functionalization by hydrogen atoms is demonstrated together with the fine tuning of multi-layer graphene resistivity as well as the transition from metallic to semiconducting behavior with a gap opening. The interaction of oxygen atoms with multilayer graphene provides a strong modification of surface wettability without significant change in conductivity, thus suggesting that oxidation effects are mainly confined on the outmost graphene. Moreover, the air exposure of graphene oxidized by plasma treatment results in peculiar chemical mechanisms with important effect on the transport properties of the material. Finally, we investigate the restoration of graphene from graphene oxide by modulated hydrogen plasma. [ABSTRACT FROM AUTHOR]

Chemical Vapor Deposited (CVD) graphene is one of the most interesting candidate to replace indium tin oxide (ITO) as transparent conductive electrode in organic photovoltaic field. Here, a four-layer graphene has been properly doped to decrease the sheet resistance down to 30 Ohm/sq and treated with PEDOT:PSS to make it compatible with the typical solution processing of this photovoltaic technology. The functionalized graphene has been applied as cathode in inverted polymer solar cells fabricated by spray coating the active layer and the transport layers. A significant power conversion efficiency of 3.1% has been achieved, not far from the reference ITO-based cells. All the process has been carried out by using commercial materials and industry-compatible solvents. Moreover, the preliminary results on the first application of graphene electrode in a module are reported. The active area of the module is 1.6 cm 2 . The electrical functionality of the module demonstrates the high quality of graphene over relatively large area and, combined with the spray technique used for the deposition of the layers, shows the potential for a real ITO-free scale-up of organic photovoltaics. [ABSTRACT FROM AUTHOR]

In this work, we detail the integration of monolayer graphene electrodes in Silicon Nitride waveguides to achieve wavelength tuning. The numerical results show that wavelength shifts of a few hundred to several thousand picometers shift can be obtained depending on the configuration. These results will help guide the design of graphene-based tunable optical devices operating in the near infrared range. [ABSTRACT FROM AUTHOR]

[Display omitted] • "Heavy" graphene doping by combining SOCl 2 and Au NPs doping methodologies. • New insights into the chemistry of graphene doping by Au NPs activated by SOCl 2. • Rs value of 35 Ω/□ for a 2L graphene while maintaining a transparency of 95%. • Graphene Rs/T performances meet the technical target required by TLC applications. The three values of transparency, conductivity and flexibility make graphene a valid alternative to replace traditional electrode materials such as indium tin oxide in electrical and optical devices. In recent years, research efforts have been addressed to investigate doping methodologies for reducing further the sheet resistance while maintaining high transparency. In this contribution, we explore the possibility to integrate both the covalent and non-covalent doping in order to increase the carrier charge density without affecting their mobility significantly. We present a new graphene doping methodology that combines the effect of SOCl 2 covalent p-doping with a synergic p-doping effect of cationic gold nanoparticles activated by the same SOCl 2 chemistry. We demonstrate that this original co-doping strategy can provide CVD graphene multilayers with record sheet resistance Rs performances, which meet the technical target required by several industrial applications. [ABSTRACT FROM AUTHOR]

In this paper, we report on the engineering and the realization of optically transparent graphene-based microwave devices using Chemical Vapour Deposition (CVD) graphene whose sheet resistance may be tailored down to values below 30 Ω/sq. In particular, we show that the process was successfully used to realize and characterize a simple, optically transparent graphene-based wire-grid polarizer at microwave frequencies (X band). The availability of graphene operating in a quasi-metallic region may allow the integration of graphene layers in several microwave components, thus leading to the realization of fully transparent (and flexible) microwave devices. [ABSTRACT FROM AUTHOR]

• Graphene is applied as top conductive electrode in silicon heterojunction solar cells. • Graphene is tested on different p-type doped Si- and SiO x -based emitters. • Results are encouraging if compared with standard top conductive electrodes. • High quality of dry-transferred graphene over large area (4 cm2) is demonstrated. • It is possible to avoid conventional plasma-based electrodes and their deleterious effect. Chemical Vapor Deposited (CVD) graphene is an attractive candidate as transparent conductive electrode (TCE) for solar cells. Here it is proposed as TCE for silicon heterojunction solar cells (Si-HJSCs) and tested over devices with area up to 4 cm2 realized on n-type c-Si wafers with three different p-type emitters facing the dry-transferred graphene stack: amorphous silicon (a-Si:H), nanocrystalline silicon (nc-Si:H), and nanocrystalline silicon oxide (nc-SiO x :H). A dependence of the cell performance on the material in contact with graphene has been observed with the most promising results in case of nc-Si:H and nc-SiO x emitter. In particular, with respect to reference cells with standard TCE a short circuit current density gain of 1.4 mA/cm2 has been achieved when including an antireflection coating. The present work demonstrates the high quality of dry-transferred CVD-graphene over relatively large area and the feasibility of Si-HJSCs integrating graphene, where the fabrication sequence asks for a transfer process that guarantees a much better contact with the underlying functional layer with respect to more common designs where graphene is transferred onto a support substrate. This approach provides a possible pathway to Si-HJSCs free from conventional plasma-based TCEs and their deleterious effects due to plasma luminescence and ion bombardment, while offering an interesting platform for getting insights in the mechanisms at play at the interfaces with graphene within Si wafer-based devices. [ABSTRACT FROM AUTHOR]